Geological Chronicle
Ansgarius is an impact crater located near the eastern limb of the Moon. When viewed from Earth, foreshortening gives the crater a highly oval shape, but the rim is actually nearly circular. The crater La Pérouse lies to the northwest, and Behaim lies to the south.
The formation dates to the Imbrian period on the lunar geologic timescale. Its rim is not significantly worn and has a terraced interior surface, with an outward notch in the north-northeastern wall. Along the southwest, the rim appears somewhat flattened rather than round and intrudes into an older formation of which little remains except the western rim. The interior floor is relatively flat, marked only by a few hills and tiny craterlets.
German astronomer Johann Mädler introduced the name into lunar nomenclature during the 19th century. The namesake is St. Ansgar, a 9th-century German theologian and Benedictine missionary monk who brought Catholicism to northern Germany and Scandinavia, known as the Apostle of the North. The International Astronomical Union formerly approved the designation in 1935.